This application claims the priority of Korean Patent Application No. 2002-32525, filed Jun. 11, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to an apparatus for connecting and disconnecting a developing bias power supply and, more particularly, to an apparatus for connecting and disconnecting a developing bias power supply in an image forming system in which a developing unit is spaced apart from a photosensitive body by a predetermined distance.
2. Description of the Related Art
In general, an electrophotographic printer such as a color laser printer, has an image forming apparatus, which forms an electrostatic latent image on a photosensitive body, develops the electrostatic latent image with toner using a developing unit, transfers the developed image onto paper via a transfer body, heats and pressurizes the paper, and completely fixes the transferred image on the paper.
FIG. 1 shows an example of an image forming system for such an electrophotographic printer.
The image forming system includes a photosensitive drum 10 as a photosensitive body; a charger 11 which charges the surface of the photosensitive drum 10 at a predetermined potential; a laser scanning unit (LSU) 12 as an exposing unit, which radiates light onto the charged photosensitive drum 10 and forms an electrostatic latent image; a developing unit 13 which develops the electrostatic latent image with toner having four colors such as yellow (Y), magenta (M), cyan (C), and black (K) into a predetermined toner image; a transfer belt 14 which sequentially overlaps the toner image having four colors developed on the photosensitive drum 10; a first transfer roller 14a which transfers the image developed on the photosensitive drum 10 onto the transfer belt 14; a second transfer roller 14b which transfers the image having four colors overlapped on the transfer belt 14 onto a piece of paper; and a fusing unit 15 which heats the paper at a predetermined temperature, pressurizes the paper and fixes the transferred image on the paper. Four developers 13-Y, 13-M, 13-C, and 13-K are provided in the developing unit 13. The four developers 13-Y, 13-M, 13-C, and 13-K are elastically biased in a direction that is spaced apart from the photosensitive drum 10 by a predetermined gap, selectively move toward the photosensitive drum 10 by rotation of cams 13b-Y, 13b-M, 13b-C and 13b-K, respectively, and allow developing rollers 13a-Y, 13a-M, 13a-C, and 13a-K, respectively, provided at a front end of the developer to contact the photosensitive drum 10. Reference numerals 16, 17, 18, and 19 denote a paper cassette, a photosensitive drum cleaning blade, an eraser, and a paper ejecting route, respectively.
In the above structure, an image forming process will be performed as described below.
If the photosensitive drum 10 is charged by the charger 11, the LSU 12 radiates light onto the photosensitive drum 10, thereby forming an electrostatic latent image of an image to be developed as a first color. For example, if an image of yellow color is first developed, the developer 13-Y of yellow color accesses the photosensitive drum 10 through being driven by a corresponding cam 13b-Y, thereby developing the electrostatic latent image formed on the photosensitive drum 10 with toner of yellow color, as shown in FIG. 2. Toner T on the outer surface of a developing roller 13a-Y is transferred to a portion of the electrostatic latent image of the photosensitive drum 10 that contacts the developing roller 13a-Y. A yellow image developed in the above manner is transferred onto the transfer belt 14 via a first transfer nip N1 (FIG. 1). Subsequently, a second color electrostatic latent image is formed by charging and exposing the photosensitive drum 10. If a second color is magenta, the developer 13-M of magenta color accesses the photosensitive drum 10, thereby developing an electrostatic latent image. A magenta image developed in this way is superimposed onto the photosensitive drum 10 and transferred onto the transfer belt 14 onto which the yellow image has been transferred. Similarly, a third image of cyan color and a fourth image of black color are developed and transferred, thereby a desired color image is finally formed on the transfer belt 14. Subsequently, the completed color image is transferred onto the paper fed to a second transfer nip N2 between the transfer belt 14 and the second transfer roller 14b, is heated and pressured by the fusing unit 15, and is completely fixed on the paper.
However, in the above structure, the four-color developers 13-Y, 13-M, 13-C, and 13-K of the developing unit 13 alternately contact with and separate from the photosensitive drum 10 to develop images. Thus, whenever the developing rollers 13a-Y, 13a-M, 13a-C and 13a-K of the developers 13-Y, 13-M, 13-C, and 13-K, respectively, collide with the photosensitive drum 10, the collision may shock the photosensitive drum 10, causing a jitter error in which an image jitters.
Accordingly, to fundamentally solve problems of the development method, it is preferable to employ a developing unit for performing a development step, in which the developers 13-Y, 13-M, 13-C, and 13-Y are secured to be spaced apart from the photosensitive drum 10 by a predetermined gap. An example thereof is shown in FIG. 3. In the description of FIG. 3, reference numerals which are the same as reference numerals used in FIG. 1 refer to the same elements as those in FIG. 1, and further descriptions thereof will be omitted.
Referring to FIG. 3, an image forming system does not include a cam which mechanically contacts each of developers 20-Y, 20-M, 20-C, and 20-K to the photosensitive drum 10, and the developers 20-Y, 20-M, 20-C, and 20-K are spaced apart from the photosensitive drum 10 by a predetermined gap. A respective toner-supplying roller, a respective seal blade, a respective doctor blade and a respective developing roller (21a-Y, 21a-M, 21a-C and 21a-K) are provided in each of the developers 20-Y, 20-M, 20-C, and 20-K. A plurality of switches (not shown) and a connection circuit are used in each of the developers 20-Y, 20-M, 20-C, and 20-K to connect a high voltage power supply to the respective developing rollers 21a-Y, 21a-M, 21a-C and 21a-K, the corresponding toner-supplying roller, and the corresponding doctor blade when the developers 20-Y, 20-M, 20-C, and 20-K are used, and to disconnect the high voltage power supply from the developing rollers 21a-Y, 21a-M, 21a-C and 21a-K, the toner-supplying rollers, and the doctor blades when the developers 20-Y, 20-M, 20-C, and 20-K are not used. Hence, the structure of each developer becomes complicated.
The present invention provides an apparatus for connecting and disconnecting a developing bias power supply that supplies a high voltage to each developer of an image forming system in which the developers are secured to be spaced apart from a photosensitive drum by a predetermined gap.
According to one aspect of the present invention, there is provided an apparatus for connecting and disconnecting a developing bias power supply in an image forming system, which operates a plurality of developers in sequence and develops an electrostatic latent image formed on a photosensitive body in a predetermined color. The apparatus comprises a plurality of electro-magnetic clutches, each clutch being provided to correspond to a respective developer to connect and disconnect driving of the respective developer. A deceleration gear assembly, which is rotated according to the rotation of a gear of the respective developer connected to the respective electro-magnetic clutch, and a connection unit, which is connected to the deceleration gear assembly, rotate to connect/disconnect a developing bias power supply to/from the respective developer.
The connection unit for connecting and disconnecting the developing bias power supply of each of the developers may comprise a cylindrical drum, conductive bands which are spaced apart from each other by a predetermined gap in a longitudinal direction of the cylindrical drum, each conductive band having a non-conductive opening or gap in a circumferential direction of the cylindrical drum, and terminals, a pair of which is formed to correspond to each of the conductive bands, to contact the conductive bands, and thus be electrically connected.
One of each pair of the terminals may be connected to one of the developers, and the other one of the pair of terminals may be connected to a high voltage power supply. The apparatus may further comprise leads which extend in a direction of the conductive bands from the terminals and contact the conductive bands.
According to another aspect of the present invention, there is provided an apparatus for connecting and disconnecting a developing bias power supply in an image forming system, which operates a plurality of developers in sequence and develops an electrostatic latent image formed on a photosensitive body in a predetermined color. The apparatus comprises a plurality of electro-magnetic clutches which are provided to correspond to a respective one of the developers and to connect and disconnect rotation of the respective one of the developers, a deceleration gear assembly, which is rotated according to the rotation of a gear of the developer connected to a respective electro-magnetic clutch, and at least one connection unit, which is connected to the deceleration gear assembly, rotates to connect the developing bias power supply to/from at least one of the developers.